Dorsal column postsynaptic tract neurons were recorded electrophysiologically in the lumbar dorsal horn of anesthetized cats. Pinch-responsive (putatively nociceptive) and pinch-nonresponsive cells were subjected to repeated noxious heat stimuli. Pinch-responsive cells were shown to have nociceptor input from high-threshold mechanoreceptive nociceptor because they responded to noxious heat only when their cutaneous receptive field had been sensitized by previous noxious heat. Pinch-noresponsive neurons did not respond to noxious heat. These experiments confirm a significant difference between rats and cats in the functional organization of a major somatosensory projection. A double label method was devised to unequivocally locate peptidergic primary afferent axon terminals within the dorsal horn. Preliminary results confirm the presence of primary afferent terminals in laminae I-II which contain substance P-like immunoreactivity.